1. Field of the Invention
This invention relates to prefabricated reinforcements for asphaltic pavings and primarily to prefabricated reinforcements incorporated in asphaltic concrete overlays used to repair cracked pavings. Typically an underlying paving, either new or in need of repair, is covered with a liquid asphaltic tack coat. After the tack coat has partially cured, the reinforcement is laid on top of it. Finally, an overlying layer of asphaltic paving is applied on top of the reinforcement. This invention also relates to processes for making and using such reinforcements.
2. Description of the Prior Art
Various methods and composites for reinforcing asphaltic roads and overlays have been proposed. Some have used narrow strips (4 to 44 inches wide) of a loosely woven fabric made of flexible fiberglass roving (weighing 24 ounces per square yard) in the repair of cracks in pavement. These are not impregnated with resin prior to being laid on the pavement, and do not have grid like openings. They are laid down on top of an asphalt tack coat, followed by application of asphaltic concrete, but they are too expensive and too flexible to be practical to lay over substantial portions of a roadway and, because of their flexibility, would be difficult to handle if installed over substantial portions of a road where they would be subjected to traffic from paving vehicles and personnel as the overlayment is put down. Also, the essentially closed nature of the fabric prevents direct contact between underlayment and overlying asphaltic layers, which may lead to slippage between the two layers.
Some in the prior art have used rigid plastic grids. These have the disadvantage that they cannot be continuously unrolled and are therefore difficult to install, and while they may use fiberglass as a filler for the plastic, they do not have the strength or other desirable characteristics of continuous filament fiberglass strands.
A European patent application, publication No. 0199827, date of publication Nov. 5, 1986, by the present inventor and assigned to the same assignee, describes glass grids impregnated with asphaltic resins, but without any adhesive coating. In order to use those grids, an asphaltic tack coat must first be applied to the roadway. The tack coat is applied as a liquid (for example, as an emulsion by spraying), and thereafter changes from a liquid to a solid -- that is, it cures. Before the tack coat is fully cured, the grid is laid on the tack coat. The tack coat partially dissolves and merges with the impregnating resin in the grid. As the tack coat cures further, it holds the grid in place on the underlying pavement. An asphaltic cement or concrete may then be applied on top of the tack coat and the grid. Tack coats have several highly desirable features for use with such reinforcements. In particular, they are completely compatible with the asphaltic concrete or cement to be used as the overlay, and equally important, their fluid nature makes them flow into, and smooth out, rough paving surfaces.
On the other hand, tack coats present several difficulties. The properties of tack coats are very sensitive to ambient conditions, particularly temperature and humidity. These conditions may affect cure temperature, and in severe conditions, they can prevent cure. In less severe circumstances, the overlay paving equipment must wait until the tack coat has cured, causing needless delays. For example, tack coats are normally emulsions of asphalt in water, often stabilized by a surfactant. To manifest their potential, the emulsion must be broken and water removed to lay down a film of asphalt. The water removal process is essentially evaporation, which is controlled by time, temperature and humidity of the environment. Frequently the environmental conditions are unfavorable, resulting in inefficient tacking or unacceptable delay.
Tack coats complicate the paving procedure in other ways as well. Not only because they require an extra-step at the paving site, but also because tack coats are generally difficult to work with. Their ability to hold the grid to the underlying paving is relatively short lived. Moreover, vehicle tires and footwear can transfer tack coat to nearby roads, and thereby to carpets and floors.